.yfb:after, .yfb:before {
  content: "";
  width: calc(100% + .04rem);
  height: .2rem;
  position: absolute;
  left: -2px;
  pointer-events: none;
}
/* .box{
  background:url("");
} */
.yfb:after{
  background: url("") no-repeat;
  background-size: 100%;
  top: -2px;
}
.yfb:before{
  background: url("") no-repeat bottom;
  background-size: 100%;
  bottom: -2px;
}